Minimal volume of amniotic fluid for reliable prenatal cytogenetic diagnosis

[The results of cytogenetic analyses in prenatal diagnosis]

INTRODUCTION

G-banding and other classical cytogenetic methods are still in use, together with molecular cytogenetic techniques such as FISH (Fluorescence In Situ Hybridization) and SKY (Spectral Karyotyping).

MATERIAL AND METHODS

This retrospective study evaluated clinical data on individuaols seeking genetic counseling over a 15-year period (1992 - 2007) at the Medical Genetic Center, Child and Youth Health Care Institute of Vojvodina in Novi Sad. The study included 37.191 genetic counselings, and 20.607 prenatal analyses (amniocentesis and cordocentesis).

RESULTS

Over a 15-year period (1992 - 2007) 17.937 amniotic fluid samples were analyzed and 274 abnormal karyotypes were found; out of 2.670 fetal blood samples, there were 78 abnormal karyotypes. During a 15-year period, prenatal diagnosis, using amniocentesis and/or cordocentesis, showed 352 fetuses with chromosomal aberrations.

DISCUSSION

On average, over the past 15-year period, 8% of pregnancies were controlled with invasive prenatal procedures. The percentage has changed; in fact, it is increasing from year to year. In 1992, only 0.82% (N=139/17000) of pregnant women in Vojvodina underwent invasive prenatal procedures, and in 2006 the rate increased to 15.65% (N=2660/17000).

CONCLUSION

It is necessary to improve and promote the possibilities of genetic counseling and invasive prenatal diagnosis in order to prevent the occurrence of chromosomal aberrations and other genetic diseases.

An absolute procedure to test the growth potential of medium and the influence of decreased oxygen tension in primary amniotic fluid cell cultures

OBJECTIVE

For prenatal cytogenetic diagnosis, cell cultures should be maximally successful. When introducing a change in conditions, e.g. a new batch of medium, the growth potential of a culture is usually compared under both the new condition and the one already in use. Such a relative test is in principle subject to drift and may over time increasingly lead to rejection of new adequate conditions, c.q. good batches of medium. We therefore wanted to design an absolute test to assess the quality of a new condition for amniotic fluid (AF) in situ cell culturing.

METHODS

We tested batches of medium under sub-optimal (stress) conditions, expecting that differences in growth potential would thereby be more readily observed. In our stress test, we diluted the culture medium to the extent of achieving a 50% growth reduction. Thresholds for rejecting a new condition were empirically determined, based on the acceptance of a less than 1% probability of false rejection of a good condition.

RESULTS

Testing three cultures per patient for ten patients, i.e. 30 cultures in total, in a medium diluted to 30% of the original concentration, showed that a minimal number of 23 successful cultures and an average number of three or more colonies per culture appeared as thresholds meeting our rejection criteria. Testing five different media resulted in the rejection of one. Using the same stress test to evaluate the effect of culturing under decreased oxygen tension showed that 2.5 and 5% oxygen tension caused a larger colony size.

CONCLUSION

We designed a sensitive absolute test to assess the quality of culturing conditions for cells to be used in prenatal diagnosis in general and in particular to test the growth potential of different batches of culture medium.

Quality aspects of prenatal cytogenetic diagnosis: determining the effect of various factors involved in handling amniotic fluid and chorionic villus material for cytogenetic diagnosis

OBJECTIVES

To investigate the effect of factors involved in cell culturing and slide preparation of amniotic fluid (AF) and chorionic villus biopsies (CVB) for prenatal cytogenetic diagnosis.

METHODS

The effect on the outcome of our standard AF cell culture procedure of volume and appearance of the submitted AF specimen, gynaecologist performing the amniocentesis, week of gestation in which the specimen was taken and culture medium was retrospectively investigated. In a prospective study controlled experimental variation was introduced in composition of fixative, relative humidity, temperature and airflow during slide preparation from primary CVB and AF in situ cultures. For evaluation, analysis of regression or variance was used.

RESULTS

Provided that at least 0.8 mL AF per culture dish was admitted, none of the investigated factors appeared as critical resulting in unacceptable variation in outcome. Variation in appearance of the AF had a relatively major impact: bloody or brown AF resulted in a 3 days longer culture time. To a limited degree, metaphase quality of AF and CVB cells was affected by composition of fixative, relative humidity, ambient temperature and airflow during slide preparation.

CONCLUSION

Current prenatal cytogenetic practice as described here appears in general to be robust and reliable. The investigated conditions are not critical within the investigated range. Expensive measures for fine control of these conditions are, therefore, not required.